1. Field of the Invention
The invention relates to a printing machine with at least two form cylinders for printing on a printing stock.
2. Discussion of the Prior Art
From U.S. Pat. Nos. 3,654,864 and 4,395,946, printing machines are known, each of which has a printing group and an imaging device. Because the imaging device, which has a laser, is arranged inside the printing machine, it is not necessary to place the printing forms into the printing machine after imaging to allow the printing process to be carried out.
From German reference DE 43 28 058 A1, printing machines are known with multiple printing groups and respective associated imaging units. In addition, the aforementioned reference depicts printing machines with drum storage units, in which a single imaging unit can image a plurality of form cylinders equipped with printing forms when the form cylinders, which have been removed from the printing machine by means of a pivoting mechanism, are arranged in the rotatable drum storage device. In another printing machine with multiple printing groups, also described in DE 43 28 058 A1, the form cylinders are removed from the printing groups by means of grippers and can then be seized by a trolley arranged on a rail that runs in the longitudinal direction of the printing machine. The trolley transports the cylinders either to an exchange device or, if the form cylinder has a renewable printing form, to an erasure and imaging device that re-images the form cylinder. After this, the form cylinder must be transported by the trolley back to the grippers, and the grippers must place the printing form back into the proper printing group.
The known methods of imaging a plurality of form cylinders thus have the disadvantage that a large number of movement steps are needed to remove the form cylinder from its mounting and, after the imaging process, to put the form cylinder back into its mounting. This procedure is not only time-consuming, but also places high demands on mechanical precision during these steps and requires that the transport steps take up relatively little time, compared with the duration of the exposure.
From German reference DE 195 12 420 A1, a sheet-fed printing machine is known with multiple form cylinders that are imaged by a single printing head. For this purpose, the printing head must be moved up to the form cylinders, one after the other, in a straight or curved line. Once again, the difficulty arises of attaining high mechanical accuracy, so that the printing forms on the form cylinders are always imaged on the same locations.
From German reference DE 195 23 378 A1, a generic printing machine is known, in which two form cylinders can be imaged by a single imaging system. The imaging system is pivoted as a unit by means of a pivoting mechanism so that both form cylinders can be imaged.
The object of the present invention is to further develop a printing machine of the type mentioned above so as to avoid mechanical inaccuracies that arise due to the transversal movement of the form cylinders or of the printing head or due to the pivotal movement of the imaging system as a whole.
Pursuant to this object, and others which will become apparent hereafter, one aspect of the present invention resides in a printing machine comprised of at least two form cylinders, at least one imaging device having a laser unit operative to emit laser pulses for imaging printing forms on the form cylinders, and light diversion means for selectively deflecting the laser pulses produced by the laser unit onto one of the at least two form cylinders.
According to the invention, light diversion means are used to optionally divert the laser pulses generated by the laser unit to one of the two or more form cylinders. The light diversion means are, for example, mirrors, prisms or optical waveguides, by means of which the laser pulse can be diverted in accordance with the curvature of the optical waveguides in any desired spatial direction.
In another embodiment of the invention the light diversion elements are associated with multiple form cylinders by pivoting, tilting or moving devices.
In yet another embodiment of the invention the laser is a semi-conductor laser.
An optical path is formed between the laser unit and the form cylinders, and optical wave guides can be arranged in this optical path.
In still another embodiment of the invention an imaging device is arranged between the form cylinders. The light diversion means, in a further embodiment can include a mirror, a prism, a system of image-forming lenses, a holographic screen or a rotary device for rotating an end of an optical wave guide directable to a surface to be printed.
In yet another embodiment of the invention a beam bundle formed by the imaging device is pivotable by the light diversion means so that the beam bundle can be directed alternately onto the circumferential surfaces of respective ones of the form cylinders.
In still another embodiment of the invention the laser unit has a modulator associated with it or the laser unit itself can be modulated.
Yet a further embodiment of the invention has a preheating unit associated with one of the form cylinders so as to heat a material on the surface of the form cylinder to be imaged to an energy level slightly below an energy level needed for application of image information. The needed level is only exceeded by the laser pulses.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of the disclosure. For a better understanding of the invention, its operating advantages, and specific objects attained by its use, reference should be had to the drawing and descriptive matter in which there are illustrated and described preferred embodiments of the invention.